Mother can execute gift deed on your favour for her 50 per cent share in flat 

2) gift deed from mother to son attracts nominal stamp duty of Rs 200 plus one per cent metro cess in muncipal corporation area 

Under the given circumstances, it's best to go for Relinquishment Deed. The Stamp Duty and Registration charges are to be nominal since your mother is relinquishing her rights over the property in your favour, being the son. The Stamp Duty and Registration charges for executing Relinquishment Deed between blood relatives will be nominal.

Between Gift Deed and Relinquishment Deed, I am of the opinion that Relinquishment Deed is preferable.

Hello,

1. A Gift Deed by your mother of the 50% she owns would be the best option.
2. As your parent is making the Gift in your favor it does not attract any stamp duty. The actual registration charge would be around Rs.500/- . Apart from this there could be charges like LBT ( LOCAL BODY TAX) of applicable which is usually 1% of the market value of the 50% of property being gifted. 
3. Although Release Deed had similar expenses, of the two Gift Deed is recommended.

Dear Client, 

Even though the legal ramifications are the same, a release deed differs greatly from a gift deed. The release deed can be drawn for cash consideration, unlike a gift deed. Every release entails a stake or interest in the property in question. There is typically a prior interest in the property held by the person in whose behalf the release is issued. With this tool, you can give another joint owner or co-owner your ownership interests in a piece of property. Transfers of this kind are final. Their main distinction is that a release deed ends a person's current rights over a specific piece of property, whereas a gift deed transfers ownership of a property to another party. A gift deed is only legally binding if it is registered, following the Transfer of Property Act of 1882. A gift deed's registration requires the donee and two witnesses to attest to it in addition to the donor's signature (required). Actually, the Gift Deed can only be enforced if it is filed with the registrar's office. In order to transfer the property as a gift, the donor must pay the stamp duty and registration fees because there is a monetary exchange involved, and the gift will be void if the donee clears it.

Hope this answer proves beneficial to you.

If you want the property to be transferred to your name then your mother should execute a registered settlement deed in your favor. 

Since this is going to be a transfer within blood relatives,  the stamp duty and the registration charges will be not more than Rs. 500.

gift deed

200 SD + 1% metro cess

registration 30k

1. You should go for release deed which will make it clear that she has gifted her share of the flat to you.

2. The stamp duty for registering Gift Deed by mother in favour of son will be negligible and it varies from State to State.

3. For your selling off the entire flat to a third party, the stamp duty will be charged on the current value of the entire flat.

- Since, your mother is joint owner of the property , and hence she should execute a registered Gift deed in your favour. 

- The stamp duty is very nominal to the tune of Rs.200/- due to being blood related , and 1% Metro Cess for Metro Development in Municipal Corporations Area and 1% Local Body Tax for Rural Area of the property .

It’s almost the same no major difference